1. Field of the Invention
The invention concerns a collector for illumination systems with a wavelength of ≦193 nm, preferably ≦126 nm, and, particularly preferred, wavelengths in the extreme ultra-violet (EUV) range. A plurality of rotationally symmetrical mirror shells is arranged concentrically around a common axis of rotation. Light, regarded as being partitioned into a plurality of ring aperture sections, is received by the plurality of mirror shells, such that one of the ring aperture sections is assigned to each mirror shell. Each of the mirror shells, in turn, irradiates a planar ring section in a plane. Thus, there is an assignment or a correspondence between a ring aperture section, a mirror shell and a planar ring section. In addition, the invention also makes available an illumination system with such a collector, a projection exposure system with an illumination system according to the invention, as well as a method for the exposure of microstructures.
2. Description of the Prior Art
Nested collectors for wavelengths of ≦193 nm, particularly wavelengths in the range of x-rays have been made known from a plurality of publications.
Thus, U.S. Pat. No. 5,768,339 shows a collimator for x-rays, wherein the collimator has several nested paraboloid-shaped reflectors. The collimator according to U.S. Pat. No. 5,768,339 serves for the purpose of forming an isotropically emitted beam bundle of an x-ray light source into a parallel beam.
A nested collector for x-rays has become known from U.S. Pat. No. 1,865,441, which serves for the purpose of collimating isotropic x-rays emitted by a source into a parallel beam bundle, as in the case of U.S. Pat. No. 5,768,339.
U.S. Pat. No. 5,763,930 shows a nested collector for a pinch-plasma light source, which serves for the purpose of collecting the radiation emitted by the light source and bundling it in a light guide.
U.S. Pat. No. 5,745,547 shows several arrangements of multichannel optics, which serve for the purpose of bundling into one point the radiation, particularly x-ray radiation, due to multiple reflections coming from a source.
In order to achieve a particularly high transmission efficiency, the invention according to U.S. Pat. No. 5,745,547 proposes elliptically shaped reflectors.
An arrangement has become known from DE 30 01 059 C2 for use in x-ray lithography systems, and this arrangement has nested parabolic mirrors arranged between the x-ray source and the mask. These mirrors are arranged in such a way that the divergent x-ray radiation will be formed into a parallel-running output beam bundle.
The arrangement according to DE 30 01 059 in turn serves only for the purpose of obtaining a good collimation for x-ray lithography.
The arrangement of nested reflectors, which has become known from WO 99/27542, in an x-ray proximity lithography system serves for the purpose of refocusing the light of a light source, so that a virtual light source is formed. The nested reflectors may have an ellipsoid form.
A nested reflector for high-energy photon sources has become known from U.S. Pat. No. 6,064,072, which serves for the purpose of shaping the divergent x-ray radiation into a parallel beam bundle.
WO 00/63922 shows a nested collector, which serves for the purpose of collimating the neutron beam.
A nested collector for x-ray radiation has become known from WO 01/08162, which is characterized by a surface roughness of the inner reflecting surface, of the individual mirror shells, of less than 12 Å rms. The collectors shown in WO 01/08162 also comprise systems with multiple reflections, particularly also Wolter systems, and are characterized by a high resolution, as is required, for example, for x-ray lithography.
For illumination optics to be used in EUV lithography, such as, for example, shown in DE 199 03 807 or WO 99/57732, in addition to resolution, high requirements are also placed on regularity or uniformity and telecentry. In such systems, the light of the light source is collected by a collector for specific light sources.